Because the petroleum source is limited, various kinds of substitutive energy are developed extensively and turned into products. Among those, the solar cell has become the commercial products for either the industrial or the residential use, and the III-V multi-junction solar cell is mainly applied to the space industry and the industrial field because of its high conversion efficiency. The structure of this kind of solar cell is a lattice-matched triple junction Ge/GaAs/GaInP structure. Ga1-xInxP (1.85 eV; x˜0.5), which is called the top cell, has the larger band gap and is the upmost layer to absorb the photon with higher energy (the wavelength from the range of the ultraviolet to the visible light); GaAs, which is called the middle cell, has the band gap with 1.42 eV and can absorb the photon with the wavelength in the near IR range; Ge, which is called the bottom cell, has the band gap with 0.74 eV and can absorb the light passed through the upper two layers with the wavelength in the IR range. Because the absorbed spectrum range is broader, the conversion efficiency is larger than 30%.